Koalas hands are one of their most important assets. If a koala was writing a bio of their best features, I’m sure they would mention their hands.
Koala hands are large and strong, with long, sharp claws, grippy palms and sensitive fingertips. They are superbly designed for climbing slippery gum-trees.
To climb, a koala places each hand on the eucalyptus trunk or branch and sinks the tips of the claws into the bark. This leaves distinctive point scratches, which are green when first made, then go brown over a few hours. The claws are long: 2-3cm each, thick: ~5mm and always sharp-pointed.
As they transfer their weight onto that hand, they grip using the granulated skin on their palm and fingers. The underside of a koala’s hand is very rough, yet pliable. Their very large paws provide a huge surface area of grip. Watch: https://youtu.be/v148yb8k2LQ
In addition, koalas have two thumbs opposing the three fingers on each hand. This gives them excellent grip around branches, and spreads their grip across a very wide area.
Koalas have extraordinary upper body strength, with very powerful hand and forearm muscles. Anyone who has ever tried to prise a koala off a tree will know this.
Occasionally a koala will slip while climbing, and leave a very distinctive large double scratch on the tree. These scratches are made by the two thumbs. If you see these, and they are about 2cm apart, they are koala scratches. If they are smaller and closer-together, they could be Brushtail or Ringtail Possum scratches – they also have two thumbs on each hand.
Even if they do slip, koalas rarely fall. I’ve seen a koala slip right off a branch, and remain hanging on with only two fingers. It easily regained its position on the branch, first strengthening its hold with the forepaw, then locking on the other hand, then raising itself on the strength of its arms and hands alone. Most koalas are so relaxed in this position that they will take the opportunity to groom their leg or flank with their other foot while hanging.
Koala hands don’t just need to be strong, they also need to be precise. To feed, a koala needs to bring small leaves on fine branches to its mouth – which can be difficult at the top of a 30metre gum tree blowing around in the wind. Often a koala is too large and heavy to reach the best leaves held on the tiniest branches, so they must manipulate branches towards themselves, while holding on in a precarious position. It is critical that they have fine control.
Possibly because of this, koalas evolved fingerprints. It is thought that fingerprints enable precise feeling that gives koalas that fine control. Koalas have evolved fingerprints independently from us and primates (the only other animals to have them), and quite recently – koala’s closest relative wombat doesn’t have them. Read more here: https://www.livescience.com/14007-koalas-human-fingerprints.html
Koala fingerprints are so similar to humans that you couldn’t tell the difference on a quick look. This is an example of convergent evolution: where two unrelated creatures develop similar features independently, from completely different backgrounds and periods of time. The evolution of flight in birds and bats is an example. https://en.wikipedia.org/wiki/Convergent_evolution
Like primates (monkeys, apes) koalas must climb trees to get food. Like great apes, they are big and heavy and don’t have a tail. Though completely unrelated, koalas and great apes (and us) have evolved to suit their fairly similar lifestyles.